This invention relates to modified polymers having useful properties as additives for lubricating oils.
The newer automobile engines place increased demands on the lubricants to be employed. In the past a number of different additives have been added to lubricating oils to improve properties such as viscosity index and dispersancy. One such additive added to lubricating oils to improve viscosity index (VI) is a two-block copolymer having the general configuration A-B where A is styrene and B is hydrogenated isoprene. These copolymer additives are further disclosed in U.S. Pat. Nos. 3,763,044 and 3,722,196, the disclosures which are herein incorporated by reference. A VI improver having greatly improved mechanical shear stability is the selectively hydrogenated star-shaped polymer disclosed in U.K. Patent Specification 1,575,507 the disclosure which is herein incorporated by reference. Employing a single additive that improves a number of lubricant properties can achieve significant reductions in cost, and also circumvent the compatibility problems that can arise between the various additives and/or base oil. However, in attempting to improve more than a single lubricant property, care must be taken in not causing the deterioration of other properties. For example, the use of an oxidation step to attach polar groups to the polymer backbone as taught in U.S. Pat. No. 3,864,268, herein incorporated by reference, leads to reduced lubricant stability by introducing additional sites for oxidative attack.
U.S. Pat. No. 4,077,893, herein incorporated by reference, discloses ashless oil-soluble additives prepared by a process comprising:
(a) reacting a selectively hydrogenated star-shaped polymer with an alpha-beta unsaturated carboxylic acid, anhydride or ester at a temperature of between about 150.degree. C. and about 300.degree. C., for between about 1 hour and about 20 hours wherein said star-shaped polymer comprises a poly (polyalkenyl coupling agent) nucleus, and at least four polymeric arms linked to said nucleus wherein said polymeric arms are selected from the group consisting of:
(i) hydrogenated homopolymers and hydrogenated copolymers of conjugated dienes; PA0 (ii) hydrogenated copolymers of conjugated dienes and monoalkenyl arenes; and PA0 (iii) mixtures thereof; PA0 (i) hydrogenated homopolymers and hydrogenated copolymers of conjugated dienes; PA0 (ii) hydrogenated copolymers of conjugated dienes and monoalkenyl arenes; and PA0 (iii) mixtures thereof; PA0 a) a long-chain alkane-substituted carboxylic acid or active derivative thereof, and PA0 b) with a C.sub.1 to C.sub.18 amine containing 1 to 8 nitrogen atoms and/or with an alkane polyol having at least two hydroxy groups; PA0 c) the preformed product of reactants a) and b). PA0 (a) hydrogenated homopolymers and hydrogenated copolymers of conjugated dienes; PA0 (b) hydrogenated copolymers of conjugated dienes and monoalkenyl arenes; and PA0 (c) mixtures thereof; PA0 (a) at least one compound of general formula EQU RO(AO).sub.n H (I) PA0 wherein R is a C.sub.4-20 alkyl group, A is an independent moiety of either ethylene or propylene, and n is an integer from 0 to 10, optionally followed by reacting with PA0 (b) a long chain alkane-substituted carboxylic acid or active derivative thereof, and/or PA0 (c) a C.sub.1 to C.sub.18 amine containing 1 to 8 nitrogen atoms and/or an alkane polyol having at least two hydroxy groups; PA0 (i) polymerizing one or more conjugated dienes in solution in the presence of an anionic initiator to form a living polymer; PA0 (ii) reacting the living polymer with a polyvinyl aromatic compound, preferably divinyl benzene, to form a star-shaped polymer; and PA0 (iii) hydrogenating the star-shaped polymer to form a hydrogenated star-shaped polymer. PA0 (a) at least one compound of general formula EQU RO(AO).sub.n H (I) PA0 wherein R is a C.sub.4-20 alkyl group, A is an independent moiety of either ethylene or propylene, and n is an integer from 0 to 10, optionally followed by reacting with PA0 (b) a long-chain alkane-substituted carboxylic acid or active derivative thereof, preferably succinic acid, anhydride or ester, and/or PA0 (c) a C.sub.1 to C.sub.18 amine containing 1 to 8 nitrogen atoms and/or with an alkane polyol having at least two hydroxy groups; or (d) the preformed product of reactants (b) and (c), optionally followed by esterifying any residual acid groups with a C.sub.1-6 alkanol. Reaction of the activated star polymer with the compound of general formula I (reactant (a)) is suitably effected by heating these reactants together, suitably at a temperature between 100.degree. C. and 200.degree. C., preferably between 140.degree. C. and 170.degree. C. Subsequent reactions with an alkane carboxylic acid (reactant (b)), and/or an alkylamine or alkane polyol (reactant (c)), or a pre-formed reaction product of (a) and (b) (reactant (d)) is suitably effected in similar manner to reaction of the activated star polymer with reactant (a), but reactants (b) and (c) may be added in any order or together. Preferably however, when both reactants (b) and (c) are used, reactant (b) is added first. The reaction may be carried out in the presence of a solvent, conveniently the same solvent as that used in the star polymer activating step 1), a lubeoil basestock being particularly convenient for both process steps. It is desirable to operate under an inert atmosphere, suitably nitrogen.
and wherein at least about 80% of the aliphatic unsaturation of the star-shaped polymer has been reduced by hydrogenation while less than 20% of the aromatic unsaturation has been reduced; and
(b) reacting the product of step (a) with an alkane polyol having at least two hydroxy groups at a temperature of between about 150.degree. C. and about 250.degree. C.
EP-A-364 058, herein incorporated by reference, published on Apr. 18, 1990 (Application ref. T 5277 EPC) describes ashless, oil-soluble additives having both dispersant and viscosity-index (VI) improving properties produced by
1) reacting an alpha-beta unsaturated carboxylic acid or active derivative thereof, preferably at a temperature of between about 100.degree. C. and about 300.degree. C. for between about 1 hour and about 24 hours, with a selectively hydrogenated star-shaped polymer comprising a polyvinyl aromatic nucleus and at least 4 polymeric arms e.g. 4-25 arms, which arms each can have a number average molecular weight of e.g. 5,000 to 150,000 and are linked to said nucleus, wherein said polymeric arms are selected from the group consisting of:
and wherein at least 80%, preferably 90 to 98%, of the aliphatic unsaturation of the star-shaped polymer has been reduced by hydrogenation while less than 20% of the aromatic unsaturation has been reduced; and
2) reacting the activated hydrogenated star polymer thus formed with:
or with